Gamma-caprolactone is commercially and industrially attractive because of its use as a flavor additive in foods and tobacco and for its potential as an intermediate for insecticides.
Gamma-caprolactone (.gamma.-caprolactone) has the structure: ##STR1## Gamma-caprolactone is also known as 4-hexalactone and 4-ethyl butyrolactone and in Chemical Abstracts, it is listed as 5-Ethyldihydro-2 (3H) furanone with a registry number of 695-06-7.
Various prior art methods exist for the production of gamma-caprolactone, but these methods are either expensive or do not produce good yields.
U.S. Pat. No. 3,944,572 to King, et al. discloses a process for the isomerization of epsilon-lactones to gammalactones. The process of King, et al. is a two-step process comprising heating epsilon-caprolactone in a vapor phase at a temperature of from 250.degree. C. to 400.degree. C. in the presence of an activated refractory oxide material catalyst such as activated alumina to produce hexenoic acid and 15-20% of gamma-caprolactone at the end of this first stage. The hexenoic acid which is a mono-unsaturated carboxylic acid is subjected to cyclising by contacting it with a catalyst comprising a strong protonating agent which may be a strong acid, a cation exchange resin in the free acid form, a strong acidic mixture containing hydrogen ions such as hydrogen halides and acetic acid or similar protonating substances.
Chemical Abstracts 76-59006d of Ger. Offen. No. 2,122,501 assigned to Rhone-Poulenc S.A. discloses the isomerization of epsilon-caprolactone in benzene in the presence of borophosphoric acid at 250.degree. C. to produce gamma-caprolactone in relatively low yields.
"Isomerization of Epsilon-Caprolactone" by Tan, et al., Hokkaido Daigaku Kogakubu Kenkyu Hokoku, 70, pp. 115-119 (1974) abstracted in Chemical Abstracts 81-135925y discloses a process for the production of gamma-caprolactone by the isomerization of epsilon-caprolactone. According to Tan, et al., epsilon-caprolactone in an aqueous solution of ammonium chloride is heated at 300.degree. C. to yield gamma-caprolactone and a small amount of delta-caprolactone. The epsilon-caprolactone isomerization can also be carried out in an aqueous solution of hydrochloric acid at 300.degree. C. The reaction yielded approximately 40% of gamma and delta-caprolactones.
While the process described by Tan, et al. yields gamma-caprolactone in a one-step isomerization process, the process, however, disadvantageously requires a relatively high temperature, i.e., about 300.degree. C., and yields gamma-caprolactone and a small amount of delta-caprolactone in only a 40% yield.